There is known a single facer which forms a single-faced corrugated board by forming a corrugated medium so as to have a corrugation with a predetermined pitch size, and providing the medium with a liner upon the crests of the corrugation by using a suitable adhesive. The single facer comprises an outer fluted roll and an inner fluted roll both having flutes upon the circumferential portions thereof and rotatably supported upon a frame in such a way that their fluted circumferences may be engaged with each other in a vertical relationship, and a press roll which is designed to be brought into press contact with the inner fluted roll through means of the corrugated medium and liner. The corrugated medium is formed so as to have predetermined flutes or corrugations as it is fed between the outer fluted roll and the inner fluted roll under engagement of their fluted circumferences, and in addition glue is applied to the crests of the corrugations by means of a gluing roll provided within a gluing mechanism. The liner being fed from the opposite side of the press roll with respect to the corrugated medium, is bonded to the crests of the corrugated medium being pressed against the lower fluted roll by means of the press roll as it passes therebetween so as to form a single-faced corrugated board.
Single-faced corrugated boards are generally classified into Flute A, Flute B, Flute C, Flute D and Flute E type boards depending upon the depth of the flutes formed upon the corrugated medium and the standard number of crests per 30 cm. Such flute type can be selected depending upon the shapes of the fluted circumferences of the outer and inner fluted rolls to be disposed within the single facer apparatus or system.
As described above, there are many flute types to be used in connection with the formation of the single-faced corrugated board and the corrugation type is dependent upon the shape of the flutes formed upon the surfaces of the outer and inner fluted rolls incorporated within the single facer. Accordingly, in order to form different types of single-faced corrugated boards in one single facer, there has been employed a constitution, in which a plurality of single facers are arranged in the corrugator line in order to facilitate selective shifting of the board components to the desired single facer.
As an example of a prior art system of arranging, for example, two single facers, there is a tandem system in which two single facers are serially arranged along the corrugator line and a double deck system in which one single facer is stacked or disposed upon top of o above the other within the corrugator line. Both of these systems involve various problems for practical applications including the installation area, workability and incidental equipment, while it is also obvious that the cost of the apparatus is almost doubled due to the use of two single facers. Thus, it is common to selectively use a pair of fluted roll units each having fluted rolls with different types of flutes disposed within one single facer so as to form two different flute types of single-faced corrugated boards.
The outer and inner fluted rolls constituting each fluted roll unit are allowed to perform normal rotation while being heated to a predetermined temperature by means of feeding steam into internal spaces thereof. Accordingly, when shifting is made from the fluted roll unit under operation to the other unit on stand-by in order to change the flute type, the pair of fluted rolls on stand-by must be preliminarily heated by means of feeding steam thereto for immediately starting formation of a single-faced corrugated board with a different flute type.
However, in the system where a pair of fluted roll units are disposed within one single facer, the outer and inner fluted rolls constituting the stand-by fluted roll unit are separated from the drive unit, so that, if steam is fed to the stand-by outer and inner fluted rolls, it is condensed into water drops which accumulate upon the lower portions thereof so as to cool such portions, leading to the disadvantageous uneven heating of the fluted rolls. Namely, if the fluted rolls are heated unevenly, they tend to exhibit a non-uniform coefficient of thermal expansion, which causes a serious problem of non-uniformity in the shape of the flutes formed along the circumferential portions thereof. Therefore, currently used techniques for changing the flute type is to first implement shifting of the system to the desired fluted roll unit; the selected fluted roll unit is then connected to the drive unit: and subsequently steam is fed to the outer and inner fluted rolls so as to heat them before starting the normal rotation thereof. However, such technique disadvantageously takes time for completing the flute type changing operation.
While the above problems can be solved by allowing the standby outer and inner fluted rolls to be disposed in an idle mode while steam is supplied thereto there remains the problem, in connection with such type of single facer having a pair of fluted roll units of actually achieving the shifting operation, for the respective fluted roll unit, between the normal rotation mode and the idling mode.